(1) Field of the Invention
This invention relates to a transmission apparatus and, more particularly, to a transmission apparatus for cross-connecting a signal.
(2) Description of the Related Art
Usually a transmission apparatus (synchronous optical network (SONET)/synchronous digital hierarchy (SDH) transmission apparatus, for example) on a ring network includes a currently used system and a spare system in case of a communication failure. Such a transmission apparatus receives a signal sent from a low-speed network at a lower layer and adds the signal to a high-speed network at a higher layer. In addition, such a transmission apparatus receives a signal sent from the high-speed network at the higher layer and drops the signal onto the low-speed network at the lower layer. Such a transmission apparatus also passes a signal it received to another transmission apparatus. An SDH frame is transmitted to a high-speed transmission line in the ring network and the signal sent from the lower layer is included in a payload of the SDH frame.
FIG. 19 shows an example of mounting units in a transmission apparatus. As shown in FIG. 19, a transmission apparatus has a shelf 100 and units such as an interface channel switch unit (IFSW) 0, an IFSW 1, an IFSW 3, interface units (INFs) 1 through 6, SYNCs 0 and 1, STS1 switch fabric units (STSSWs) 0 and 1, a CPU, a HUB, and a DCC are mounted. STS1 stands for Synchronous Transport Signal Level 1.
As will be described later, the IFSW 0, the IFSW 1, and the IFSW 3 are units for switching units from a currently used system to a spare system in the case of a unit failure. The INFs 1 through 6 are interface units for sending and receiving optical or electrical signals. The SYNCs 0 and 1 are units for generating a synchronizing clock for each unit. As will be described later, each of the STSSWs 0 and 1 is a unit including a switch fabric and a cross connect. The CPU is a control unit for controlling each unit. The HUB is an alarm unit for orderwire (OW)/housekeeping (HK)/office. The DCC is a unit for a data communication channel (DCC). The transmission apparatus includes the above units for performing communication.
As stated above, the transmission apparatus has a mechanism which can deal with failure. The transmission apparatus includes line redundancy for dealing with a line failure, unit redundancy for dealing with a unit failure, and a path redundancy for dealing with a path failure as applications for dealing with failure.
FIG. 20 is a view for describing one-plus-one line redundancy. In FIG. 20, two transmission apparatus installed in a and b stations are shown. In FIG. 20, each of the two transmission apparatus includes only INFs 1 through 3 and a switch fabric included in an STSSW 0 as a result of simplifying the transmission apparatus shown in FIG. 19. W (work) and P (protect) shown in each INF 1 and each INF 2 in FIG. 20 indicate a currently used system and a spare system respectively.
With the one-plus-one line redundancy, a unit which belongs to the currently used system and a unit which belongs to the spare system send signals and a switch fabric at the receiving end switches a signal to be received and receives it.
For example, the switch fabric included in the transmission apparatus installed in the a station receives a signal sent from a tributary side (lower layer side) by the INF 3 and outputs it to both of the INFs 1 and 2. That is to say, the transmission apparatus installed in the a station outputs the signal to 0-system and 1-system lines on a line side (higher layer side). The switch fabric included in the transmission apparatus in the b station at the receiving end switches a switch (indicated by SW in FIG. 20) for outputting the signals sent via the 0-system and 1-system lines to the INF 3. Similarly, the switch fabric included in the transmission apparatus installed in the b station outputs a signal which is sent from a tributary side and which is received by the INF 3 to both of the INFs 1 and 2. The switch fabric included in the transmission apparatus in the a station at the receiving end switches a switch for outputting the signals sent via the 0-system and 1-system lines to the INF 3.
Accordingly, if a failure occurs in the 0-system line which belongs to the currently used system, then the switch fabric included in the transmission apparatus installed in the a or b station switches the switch. By doing so, a signal is received from the 1-system line which belongs to the spare system, and the failure is dealt with.
FIG. 21 is a view for describing one-to-one line redundancy. The one-to-one line redundancy differs from the one-plus-one line redundancy shown in FIG. 20 in switch structure in a switch fabric. Only descriptions of the switch fabric will be given.
With the one-plus-one line redundancy, signals are sent from the INFs 1 and 2 which belong to the currently used system and the spare system, respectively, and a signal to be received is selected at the receiving end. With the one-to-one line redundancy, on the other hand, the switch fabric includes a switch so that the sending of a signal can also be selected at the sending end.
For example, a switch fabric included in a transmission apparatus installed in an a station receives a signal from a tributary side (INF 3) and outputs it only to an INF 1. If a failure occurs in a 0-system line, then the switch fabric switches a switch (indicated by BR in FIG. 21) for outputting the signal received from the INF 3 to an INF 2. In addition, the switch fabric switches a switch (indicated by SW in FIG. 21) to the INF 2 side so that it can receive a signal sent from a transmission apparatus installed in a b station. With the one-to-one line redundancy, the switches included in the switch fabric at the sending and receiving ends are switched in this way for dealing with the line failure.
FIG. 22 is a view for describing one-to-N line redundancy. Unlike the one-to-one line redundancy, a plurality of lines which belong to a currently used system are used in the case of the one-to-N line redundancy. In FIG. 22, for example, INFs 2 and 3 belong to a currently used system and there are two 0-system lines. If a failure occurs in one of the two 0-system lines, a switch fabric switches switches (indicated by SW and BR in FIG. 22) so that it can communicate via a 1-system line.
Unit redundancy will now be described. FIG. 23 is a view for describing one-plus-one unit redundancy. In FIG. 23, two transmission apparatus installed in a and b stations are shown. In FIG. 23, each of the two transmission apparatus includes only INFs 1 through 3, a switch fabric included in an STSSW 0, and an IFSW 0 as a result of simplifying the transmission apparatus shown in FIG. 19.
The IFSW 0 is a unit for dealing with a unit failure. For example, the INF 3 included in the transmission apparatus installed in the a station receives a signal sent from a line side. The switch fabric outputs the signal received by the INF 3 to both of the INFs 1 and 2 which belong to a currently used system and a spare system respectively. Switches included in the IFSW 0 select only the signal outputted to the INF 1 which belongs to the currently used system, and send the signal to the transmission apparatus installed in the b station. In addition, the IFSW 0 included in the transmission apparatus installed in the a station outputs a signal received from a tributary side to both of the INFs 1 and 2 which belong to the currently used system and the spare system respectively. Switches included in the switch fabric select the signal outputted to the INF 1 which belongs to the currently used system, and output the signal to the INF 3. The operation of the transmission apparatus installed in the b station is the same as that of the transmission apparatus installed in the a station.
It is assumed that a failure occurs in the INF 1 in the a station which belongs to the currently used system. The IFSWs 0 and the switch fabrics included in the transmission apparatus installed in the a and b stations switch the switches so that a signal will be sent or received by the INF 2 which belongs to the spare system. With the unit redundancy, a communication failure on the tributary side is dealt with.
FIG. 24 is a view for describing one-to-one unit redundancy. The one-to-one unit redundancy differs from the one-plus-one unit redundancy shown in FIG. 23 in switch structure in a switch fabric and an IFSW 0. Only descriptions of the switch fabric and the IFSW 0 will be given.
With the one-plus-one unit redundancy, the switch fabric outputs signals to INFs 1 and 2 which belong to a currently used system and a spare system, respectively, and the IFSW 0 selects a signal to be sent to the receiving end. With the one-to-one unit redundancy, on the other hand, the switch fabric includes a switch (indicated by BR in FIG. 24) so that the sending of a signal can also be selected at the sending end. In addition, the IFSW 0 includes a switch (indicated by BR in FIG. 24) so that it can output a signal it received to one of INFs 1 and 2.
For example, a switch fabric included in a transmission apparatus installed in an a station receives a signal sent from a line side by an INF 3 and outputs it only to an INF 1. An IFSW 0 outputs a signal it received from a transmission apparatus installed in a b station to the INF 1.
If a failure occurs in the INF 1, then the switch fabric switches the BR shown in FIG. 24 to the INF 2 which belongs to a spare system. The IFSW 0 switches SW to the INF 2 side so that a signal outputted from the INF 2 which belongs to the spare system will be sent to the transmission apparatus installed in the b station at the receiving end. In addition, the IFSW 0 switches the BR so that a signal sent from the transmission apparatus installed in the b station will be outputted to the INF 2. The switch fabric switches SW so that the signal sent from the INF 2 will be outputted to the INF 3.
With the one-to-one unit redundancy, switches included in a switch fabric and an IFSW 0 at the sending or receiving end are switched in this way to deal with a unit failure.
FIG. 25 is a view for describing one-to-N unit redundancy. Unlike the one-to-one unit redundancy, a plurality of INF units are used in the case of the one-to-N unit redundancy. In FIG. 25, for example, INFs 2 and 3 belong to a currently used system. If a failure occurs in one of the INFs 2 and 3 which belong to the currently used system, a switch fabric and an IFSW 0 switch SWs and BRs shown in FIG. 25 so that communication can be performed by using an INF 1 which belongs to a spare system.
Path redundancy will now be described. FIG. 26 is a view for describing path redundancy in a UPSR. In FIG. 26, four transmission apparatus installed in a, b, c, and d stations are shown. In FIG. 26, each of the four transmission apparatus includes only INFs 1 through 3 and an STSSW 0 as a result of simplifying the transmission apparatus shown in FIG. 19. WESTs and EASTs shown in FIG. 26 indicate INFs which make up a ring network.
With the path redundancy in a uni-direction protection switched ring (UPSR), the same signal is sent via paths which belong to a currently used system and a spare system. One signal is selected and received at the receiving end. For example, it is assumed that the transmission apparatus installed in the c station receives a signal sent from a tributary side by an INF 3. An STSSW 0 included in the transmission apparatus installed in the c station sends the signal received by the INF 3 from both of INFs 1 and 2 with a cross connect. Cross connects in STSSWs 0 included in the transmission apparatus installed in the b and d stations are set so that the signals received from the c station will pass through the STSSWs 0. A cross connect in an STSSW 0 included in the transmission apparatus installed in the a station is set so that the STSSW 0 will receive only the signal sent from the b station and so that the STSSW 0 will output the signal to an INF 3. As a result, the route from the c station, through the b station, to the a station is a path which belongs to a currently used system, and the route from the c station, through the d station, to the a station is a path which belongs to a spare system. Therefore, if a failure occurs in the path between the b and a stations (indicated by a dotted-line circle in FIG. 26) along which a signal is sent, then the STSSW 0 included in the transmission apparatus installed in the a station receives a signal sent from the d station. By doing so, the path failure can be dealt with.
FIG. 27 is a view for describing path redundancy in a BLSR. With a bidirection line switched ring (BLSR), a path is divided into a currently used system and a spare system. With an OC(optical carrier level)-48 BLSR, 48 channels are divided into, for example, 1 through 24 channels and 25 through 48 channels as a currently used system and a spare system respectively. In FIG. 27, a solid arrow indicates 1 through 24 channels which belong to the currently used system, and a dotted-line arrow indicates 25 through 48 channels which belong to the spare system.
It is assumed that a transmission apparatus installed in a c station receives a signal sent from a tributary side by an INF 3. An STSSW 0 included in the transmission apparatus installed in the c station sends the signal received by the INF 3 from an INF 2 with a cross connect. A cross connects in an STSSW 0 included in a transmission apparatus installed in a b station is set so that the signal received from the c station will pass through the STSSW 0. A cross connect in an STSSW 0 included in a transmission apparatus installed in an a station is set so that the STSSW 0 will receive the signal sent from the b station and so that the STSSW 0 will output the signal to an INF 3.
If a failure occurs in the path between the b and a stations (dotted-line circle in FIG. 27) along which a signal is sent, then the STSSW 0 included in the transmission apparatus installed in the b station makes a signal sent from the c station turn back to the c station by using a path which belongs to the spare system. The STSSW 0 included in the transmission apparatus installed in the c station sends the signal sent from the b station to the d station. The d station sends the signal sent from the c station to the a station. By doing so, the path failure can be dealt with.
Operation which is performed if a failure occurs will now be described in detail. FIG. 28 is a view for describing the details of the one-to-one line redundancy. In FIG. 28, the structure of the transmission apparatus in the a station shown in FIG. 21 is shown. INFs 1a and 1b correspond to an optical/electrical (O/E) converter and an E/O converter, respectively, included in the INF 1 and the INFs 1a and 1b make up the INF 1. Similarly, INFs 2a and 2b correspond to an O/E converter and an E/O converter, respectively, included in the INF 2 and INFs 3a and 3b correspond to an O/E converter and an E/O converter, respectively, included in the INF 3. An STSSW 0 includes switch fabrics 111a and 111b, ring switches 112a and 112b, and a cross connect 113.
A solid arrow A101 in FIG. 28 indicates a signal route in the transmission apparatus in the a station in FIG. 21 which is used if a failure does not occur. A dotted-line arrow A102 in FIG. 28 indicates a signal route in the transmission apparatus in the a station in FIG. 21 which is used if a failure occurs. With the line redundancy, the settings of the ring switches 112a and 112b and the cross connect 113 are not changed. By switching switches included in the switch fabrics 111a and 111b, a signal route is switched from the 0 system which is the currently used system to the 1 system which is the spare system. The same applies to the one-plus-one line redundancy and the one-to-N line redundancy. That is to say, by switching switches included in switch fabrics 111a and 111b, a signal route is switched from the 0 system which is the currently used system to the 1 system which is the spare system.
FIG. 29 is a view for describing the details of the one-plus-one unit redundancy. In FIG. 29, the structure of the transmission apparatus installed in the a station shown in FIG. 23 is shown. Components in FIG. 29 that are the same as those shown in FIG. 28 are marked with the same symbols and descriptions of them will be omitted.
IFSWs 0a and 0b shown in FIG. 29 correspond to the IFSW 0 shown in FIG. 23. As described in FIG. 23, the IFSW 0a outputs a signal sent from the b station to both of the INFs 1 and 2 (INFs 1a and 2a). A switch fabric 111a outputs the signal outputted from the INF 1a which belongs to a currently used system to an INF 3b via a cross connect 113. A signal received by an INF 3a is outputted to both of INFs 1b and 2b by a switch fabric 111b and is outputted to the IFSW 0b. The IFSW 0b selects the signal outputted from the INF 1b and outputs it to the tributary side (b station).
If a failure occurs in the INF 1, then the switch fabric 111a selects a signal outputted from the INF 2a (shown by a dotted-line arrow A111) and outputs the signal to the INF 3b. In addition, the IFSW 0b selects a signal outputted from the INF 2b (shown by a dotted-line arrow A112) and outputs the signal to the tributary side. With the unit redundancy, the settings of ring switches 112a and 112b and a cross connect 113 are not changed. By switching switches included in the switch fabrics 111a and 111b and the IFSWs 0a and 0b, a unit is switched from the INF 1 which belongs to a currently used system to the INF 2 which belongs to a spare system. The same applies to the one-to-one unit redundancy and the one-to-N unit redundancy. That is to say, by switching switches included in switch fabrics 111a and 111b and IFSWs 0a and 0b, a unit is switched from an INF 1 which belongs to a currently used system to an INF 2 which belongs to a spare system.
FIG. 30 is a view for describing the details of the path redundancy in a UPSR. In FIG. 30, the structure of the transmission apparatus in the a station shown in FIG. 26 is shown. Components in FIG. 30 that are the same as those shown in FIG. 28 are marked with the same symbols and descriptions of them will be omitted.
A cross connect 113 shown in FIG. 30 outputs a signal which is sent from a tributary side and which is received by an INF 3a to INFs 1b and 2b. As a result, the signal received by the INF 3a is outputted from both of the EAST and WEST sides shown in FIG. 26. Of signals sent to both of INFs 1a and 2a, the cross connect 113 outputs only the signal sent to the INF 1a to an INF 3b. This signal is outputted to a tributary side.
If a path failure occurs as shown by the dotted-line circle in FIG. 26, then the cross connect 113 outputs a signal sent to the INF 2a to the INF 3b (shown by a dotted-line arrow A121). By doing so, the path failure can be dealt with.
An SDH transmission method and apparatus in which circuits in a cross connect and a path protection are simplified by controlling a read address with the same dual port random access memory (RAM) are disclosed (see, for example, Japanese Patent Laid-Open Publication No. 2005-45573). Furthermore, a method for performing cross-connecting by selecting line setting information used for a path switch service selector and by using this information is disclosed (see, for example, Japanese Patent Laid-Open Publication No. 2000-197167).
By the way, an STSSW 0 includes a plurality of switches so that various redundancy requests (line redundancy, unit redundancy, and path redundancy) made by users can be handled. Accordingly, there are unnecessary switches, depending on the type of redundancy. As shown in FIG. 30, for example, when a request for path redundancy is made to the transmission apparatus, switches included in switch fabrics 111a and 111b and ring switches 112a and 112b are not switched. Therefore, these switches are unnecessary.